The present invention relates generally to a new and improved cuvette cartridge for use with a chemical and microbiological analysis apparatus and to a method of transferring biological or other fluid from a growth or filling chamber in the cartridge to a plurality of cuvettes.
Biological fluid analyzer apparatus, such as disclosed in U.S. Pat. No. Re. 28,800 and U.S. Pat. No. 3,718,439, are capable of performing antibiotic susceptibility testing, medical bacteriology procedures, clinical chemical analysis and other related procedures. When an evaluation is undertaken with this apparatus, a biological fluid to be evaluated, such as serum, plasma, urine, cerebrospinal fluid is inoculated into an artificially prepared nutrient of reagent fluid and placed into a cuvette cartridge of the type disclosed and claimed in Acker et al. U.S. Pat. No. 4,013,368. The prior art cartridge includes a growth chamber and a plurality of cuvettes disposed below the chamber. Fluid communication means are provided between the chamber and cuvettes to allow fluid to be transferred from the chamber to each of the cuvettes.
Impregnated paper discs or a lyophilized antibiotic agent or other desired reagent are located in the cuvettes.
The cartridge is placed in the analyzer apparatus, and a pressure or vacuum source is utilized to create a pressure differential sufficient to allow the fluid in the cartridge growth chamber to pass into each of the cuvettes. Gas in the cuvettes is evacuated through a gas pervious membrane.
Once the fluid is in the cuvettes, the antibiotic or reagent in the disc becomes rehydrated and forms an antibiotic and media/micro-organism suspension. The bacterial growth rate for the fluid in the various cuvettes can then be monitored by means of a plurality of individual optical detector systems, each of which is in registration with its respective cuvette.
Electronic computation means such as computers and/or other computing devices well known in the art, are available to evaluate the output of the detection system and to make appropriate calculations, either through analog or digital means, to record and display the results in a meaningful and appropriate manner. These results include, for example, the changes in the growth rate in each cuvette and the relative changes between the control cuvette containing no antibiotic and the sample cuvettes.
Unfortunately, cuvette cartridges presently employed with fluid analyzer apparatus available in the art are not entirely satisfactory for a number of reasons. Initially, cuvette cartridges presently known in the art are costly due to their particular physical structures, the relatively complex manufacturing procedures associated with making the cartridges and the quality control procedures required to assure the desired cartridge quality. These factors are all significant when it is considered that the cartridge is a disposable type device generally associated with a one time use.
For example, one cuvette cartridge known in the art and disclosed in U.S. Pat. No. 4,013,368 utilizes a resilient unidirectional valve and a gas permeable tubular member as part of its system for transporting fluid from a growth chamber to a plurality of cuvettes. This particular structure has not been entirely satisfactory because of the expense associated with the materials utilized to make the cartridge and because the gas permeable member is not always uniform in its structural characteristics along its length, a drawback which not only adversely affects gas removal from the system but also dictates increased quality control procedures.
Another cuvette cartridge which is known in the art is a membrane type cuvette cartridge. In this particular embodiment, a chamber, located above the cuvettes, is partitioned to form two compartments. One compartment serves as a fluid growth chamber while the remaining compartment serves as a vacuum compartment. A partition, which separates the upper chamber compartments from the lower cuvettes, has openings which serve as passages for biological fluid being evaluated and for gas which is evacuated from the cuvettes. A hydrophobic membrane strip is affixed to the top surface of the separating partition so that it covers the various openings in the bottom wall of one chamber compartment and a hydrophobic membrane strip also is affixed to the bottom wall in the remaining chamber compartment. In operation, air in the cuvette is evacuated from the cuvette into the vacuum compartment while the fluid is forced through the hydrophobic membrane strip into each of the cuvettes.
Problems, aside from manufacturing and quality control problems, exist with the membrane type cuvette cartridge. The membrane type cuvette cartridges presently available have been designed to substantially fill the cuvettes with fluid. However, various applications require that air be present in the cuvettes, inasmuch as many bacteria require oxygen for growth. Efforts to provide uniform air bubbles in the cuvettes of the membrane type cuvette cartridge have been unsuccessful. Because of the particular physical characteristics of the membrane at the location of the opening to each cuvette, the air flow through the membrane into each of the cuvettes varies substantially. As a result air will flow into one cuvette easier than it will flow into another cuvette due to the impedance caused by the structure of the membrane strip. The difference in impedance of the membrane at the various openings to each of the cuvettes causes non-uniform air bubbles in the cuvettes.
Another disadvantage that sometimes occurs with the utilization of the membrane strip is that the fluid located in the interstices of the membrane strip creates a hydraulic lock so that air cannot pass into the cuvettes. As a result, the bacteria in the fluid located in the cuvettes is starved of oxygen, thereby adversely affecting bacterial growth in the cuvette.
What is desired is a cuvette cartridge in which the individual cuvettes can be filled without the cost, assembly and quality control problems associated with cartridges presently available. Moreover, it is desired to have a cuvette cartridge in which the cuvettes are not completely filled, but instead have a relatively uniform amount of air available in each cuvette to permit proper growth of the bacteria when it is located in the cuvettes.